Fluid streams, such as gases and liquids, often carry contaminant material therein. In many instances, it is desirable to filter some or all of the contaminant material from the fluid stream. For example, particulate contaminants are often present in air streams to engines for motorized vehicles and for power generation equipment, air and gas streams to gas turbine systems, air and gas streams to various combustion furnaces, and air and gas streams to heat exchangers (e.g., heating and air conditioning). Liquid streams in engine lube systems, hydraulic systems, coolant systems and fuel systems, can also carry contaminants that should be filtered. It is preferred for such systems that selected contaminant material be removed from the fluid (or have its level reduced in the fluid). A variety of fluid filters (gas or liquid filters) have been developed for contaminant reduction. In general, however, continued improvements are sought.
Pleated filtration media has been in use for many years, and is widely adopted for fluid filtration applications, including gas and liquid filtration. Pleated filtration media provides a relatively large media surface area in a given volume by folding the media back and forth such that a large amount of media can be arranged in a relatively small volume. Pleated media is typically formed from continuous or rolled webs of filter media, with the pleats formed perpendicular to the machine direction of the media. The machine direction of the media generally refers to the continuous direction of the media as it comes from a source, such as a supply roll. The continuous direction is also sometimes referred to as the machine direction of the media. The pleat folds, therefore, are generally transverse to the continuous direction of the media. In general, a first set of pleat folds forms a first face of the media pack and a second set of pleat folds forms a second face of the media pack, with the first and second pleat folds alternating with one another. It will be understood that in certain embodiments the “face” described herein can be substantially uneven or irregular, and can be planer or non-planer.
One challenge to designing filter elements containing pleated filter media is that an undesirable level of fluid flow restriction can occur as the number of pleats within a given volume increases. This restriction becomes critical as the pleats are pressed too close to each other, which can cause significant interference with filter performance. For example, pleats can be so close together that it is difficult for a fluid to enter the area between the pleats. Due to this restriction, the media in some prior pleated filters is modified to create an uneven surface with raised areas of shallow repeating arcs along the media surface. As pleats having this uneven surface become pressed toward one another, the raised areas on the media help maintain fluid flow between pleat surfaces by forming channels which aid fluid flow. Although pleats with uneven surfaces can provide advantages, the improvement is limited, especially with deeper pleat constructions.
Therefore, a need exists for improved pleated filtration media.